Process for the conversion of hydrocarbons to oxygenates

ABSTRACT

Process for converting a hydrocarbon feedstock into alcohol(s), wherein the hydrocarbons are first converted into syngas, which is subsequently converted into alcohols. The process comprises the consecutive steps of 1) converting a hydrocarbon feedstock, in a syngas reactor, into a stream A, comprising essentially of a mixture of carbon oxide(s) and hydrogen, 2) converting at least part of stream A, in the presence of a catalyst in a oxygenate synthesis reactor under a temperature comprised between 150 and 400° C. and a pressure of 20 to 200 bar, into an alcohols stream B, comprising essentially methanol, ethanol, propanol(s), H2, C1-03 alkanes, CO, CO2 and water, 3) separating stream B, into a stream C containing the CO, C1-C3 alkanes, H2 and methanol; a stream D containing the CO2; and recovering a stream E containing the ethanol, propanol(s) and water, 4) treating a fraction of stream C in order to separate said fraction into a stream comprising CO, and a stream comprising H2 and the C1-C3 alkanes, 5) reintroducing at least part of stream C together with the stream comprising CO from step 4 into the oxygenate synthesis reactor of step 2, and 6) reintroducing at least part of stream D into the syngas reactor of step 1.

This application is the U.S. national phase of International ApplicationNo. PCT/GB2007/003974 filed 17 Oct. 2007, which designated the U.S. andclaims priority to Europe Application No. 06255402.7 filed 20 Oct. 2006,the entire contents of each of which are hereby incorporated byreference.

The present invention relates to an improved process, that has asignificantly reduced level of carbon oxide(s) emissions, for theconversion of hydrocarbons into alcohol(s), wherein the hydrocarbons arefirst converted into syngas which is then subsequently converted intoalcohol(s) in the presence of a catalyst.

In particular, the present invention relates to an improved process,that has a significantly reduced level of carbon oxide(s) emissions, forthe conversion of hydrocarbons into alcohol(s), wherein the hydrocarbonsare first converted into syngas, which is then subsequently convertedinto alcohol(s) in the presence of a modified molybdenum sulphide basedcatalyst, or a modified methanol based catalyst and/or a modifiedFischer-Tropsch catalyst and/or a supported rhodium catalyst.

BACKGROUND OF THE INVENTION

In recent years increased use and demand for alcohols such as methanol,ethanol and higher alcohols has led to a greater interest in processesrelating to alcohol production. The said alcohols may be produced by thefermentation of, for example, sugars and/or cellulosic materials.

Alternatively, alcohols may be produced from synthesis gas. Synthesisgas refers to a combination of hydrogen and carbon oxides produced in asynthesis gas plant from a carbon source such as natural gas, petroleumliquids, biomass and carbonaceous materials including coal, recycledplastics, municipal wastes, or any organic material. Thus, alcohol andalcohol derivatives may provide non-petroleum based routes for theproduction of valuable chemicals and fuels.

Generally, the production of alcohols, for example methanol, takes placevia three process steps: synthesis gas preparation, methanol synthesis,and methanol purification. In the synthesis gas preparation step, anadditional stage maybe employed by where the feedstock is treated, e.g.the feedstock is purified to remove sulphur and other potential catalystpoisons prior to being converted into synthesis gas. This treatment canalso be conducted after syngas preparation; for example, when coal orbiomass is employed.

The reaction to produce alcohol(s) from syngas is generally exothermic.The formation of C2 and C2+ alcohols is believed to proceed via theformation of methanol for modified methanol catalysts and cobaltmolybdenum sulphide catalysts. However, the production of methanol isequilibrium limited and thus requires high pressures in order to achieveviable yields. Hence, pressure can be used to increase the yield, as thereaction which produces methanol exhibits a decrease in volume, asdisclosed in U.S. Pat. No. 3,326,956. Improved catalysts have nowallowed viable rates of methanol formation to be achieved at reducedreaction temperatures, and hence allow commercial operation at lowerreaction pressures, e.g. a copper oxide-zinc oxide-alumina catalyst thattypically operates at a nominal pressure of 5-1 MPa and temperaturesranging from approximately 150 DEG C. to 450 DEG C. over a variety ofcatalysts, including CuO/ZnO/Al2O3, CuO/ZnO/Cr2O3, ZnO/Cr2O3, andsupported Fe, Co, Ni, Ru, Os, Pt, and Pd catalysts. A low-pressure,copper-based methanol synthesis catalyst is commercially available fromsuppliers such as BASF, ICI Ltd. of the United Kingdom, andHaldor-Topsoe. Methanol yields from copper-based catalysts are generallyover 99.5% of the converted CO+CO2 present. Water is a by-product of theconversion of CO2 to methanol and the conversion of CO synthesis gas toC2 and C2+ oxygenates. In the presence of an active water gas-shiftcatalyst, such as a methanol catalyst or a cobalt molybdenum catalystthe water equilibrates with the carbon monoxide to give CO2 andhydrogen. A paper entitled, “Selection of Technology for Large MethanolPlants,” by Helge Holm-Larsen, presented at the 1994 World MethanolConference, Nov. 30-Dec. 1, 1994, in Geneva, Switzerland, reviews thedevelopments in methanol production and shows how further reduction incosts of methanol production will result in the construction of verylarge plants with capacities approaching 10,000 metric tonnes per day.

Other processes, for the production of C2 and C2+ alcohol(s), includethe processes described hereinafter; U.S. Pat. No. 4,122,110 relates toa process for manufacturing alcohols, particularly linear saturatedprimary alcohols, by reacting carbon monoxide with hydrogen at apressure between 20 and 250 bars and a temperature between 150 DEG and400 DEG C., in the presence of a catalyst, characterized in that thecatalyst contains at least 4 essential elements: (a) copper (b) cobalt(c) at least one element M selected from chromium, iron, vanadium andmanganese, and (d) at least one alkali metal.

U.S. Pat. No. 4,831,060 relates to the production of mixed alcohols fromcarbon monoxide and hydrogen gases using a catalyst, with optionally aco-catalyst, wherein the catalyst metals are molybdenum, tungsten orrhenium, and the co-catalyst metals are cobalt, nickel or iron. Thecatalyst is promoted with a Fischer-Tropsch promoter like an alkali oralkaline earth series metal or a smaller amount of thorium and isfurther treated by sulfiding. The composition of the mixed alcoholsfraction can be selected by selecting the extent of intimate contactamong the catalytic components.

Journal of Catalysis 114, 90-99 (1988) discloses a mechanism of ethanolformation from synthesis gas over CuO/ZnO/Al2O3. The formation ofethanol from CO and H2 over a CuO/ZnO methanol catalyst is studied in afixed-bed microreactor by measuring the isotopic distribution of thecarbon in the product ethanol when 13C methanol was added to the feed.

At present, there are two major issues, associated with the conversionof hydrocarbons to alcohol(s), which need to be addressed.

The first issue is primarily an environmental concern, as whenmanufacturing and using syngas as part of an integrated process, thehigh temperatures necessary for syngas formation, are often generated bythe burning of carbonaceous fuel, and hence dilute carbon dioxide isproduced as a result.

In addition to this, is the fact that water is produced as a result ofthe conversion of syngas to C2 and C2+ alcohol(s), which consequently israpidly converted to carbon dioxide and hydrogen during the oxygenatesynthesis reaction stage due to the nature of the typical catalysts used(i.e. active water gas-shift catalysts), and the reaction conditionstypically employed in these processes. Hence, during the overallintegrated process, significant amounts of carbon dioxide is producedand emitted into the environment.

Contributing significantly to the above issue, is the factor that theuse of a typical higher alcohol catalysts during the alcohol synthesisstage of the process, results in the build up of alkanes (due to loss ofselectivity) during the required gas recycling process, which will oftennecessitate in a purge. Typically purge streams are fuelled or flaredwhich can add significant amounts of CO2 to the overall carbonemissions.

The level of carbon dioxide present in the atmosphere is a welldocumented environmental concern of today's world, as carbon dioxide isconsidered to be the most prominent of all the ‘greenhouse gases’, andtherefore one of the main pollutants in the present atmosphere. For thisreason, it is of global interest and concern to reduce carbon dioxideemissions in industrial processes to a minimum as far as possible.

The second issue associated with the conversion of hydrocarbons toalcohol(s), wherein the hydrocarbons are first converted into syngas,which is then subsequently converted into alcohol(s), is concerned withthe overall heat efficiency of the process. Historically, there has beena lot of interest shown in trying to utilise the heat generated duringthe syngas to alcohol(s) conversion stage efficiently, for example bygenerating steam from the excess heat and subsequently using the steamto provide the energy to power alternative processes. However, dependingon the production site in question, this is not always possible.Therefore, recently more interest has been shown in trying to improveefficiency of the heat generated in a more local manner, i.e. as part ofan integrated process.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to address the aboveissues, and to provide an improved process in terms of CO2 emissions andenergy efficiency for the conversion of hydrocarbons into alcohols,wherein the hydrocarbons are first converted into syngas, which issubsequently converted into alcohols.

In particular, the present invention relates to an improved process interms of CO2 emissions and energy efficiency for the conversion ofhydrocarbons into alcohols, wherein the hydrocarbons are first convertedinto syngas, which is subsequently converted into alcohols preferably inthe presence of a modified molybdenum sulphide based catalyst, or amodified methanol based catalyst and/or a modified Fischer-Tropschcatalyst and/or a supported rhodium catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, represents one embodiment of a process scheme according to thepresent invention. This said embodiment comprises process stepsaccording to the present invention. The letter references in FIG. 1correspond to those used in the present description and appendingclaims.

FIG. 2, represents another embodiment of a process scheme according tothe present invention. This said embodiment comprises optional and/orpreferred process steps according to the present invention. The letterreferences in FIG. 2 correspond to those used in the present descriptionand appending claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention thus provides a process for the conversion of ahydrocarbon feedstock into alcohol(s), wherein the hydrocarbons arefirst converted into syngas, which is subsequently converted intoalcohols, characterised by the following consecutive steps:

-   -   1. converting a hydrocarbon feedstock, in a syngas reactor, into        a stream A, comprising essentially of a mixture of carbon        oxide(s) and hydrogen,    -   2. converting at least part of stream A, in the presence of a        catalyst in a oxygenate synthesis reactor under a temperature        comprised between 150 and 400° C. and a pressure of 20 to 200        bar, into an alcohols stream B, comprising essentially methanol,        ethanol, propanol(s), H2, C1-C3 alkanes, CO, CO2 and water,    -   3. separating stream B, into a stream C containing the CO, C1-C3        alkanes, H2 and methanol; a stream D containing the CO2; and        recovering a stream E containing the ethanol, propanol(s) and        water,    -   4. treating a fraction of stream C in order to separate said        fraction into a stream comprising CO, and a stream comprising H2        and the C1-C3 alkanes,    -   5. reintroducing at least part of stream C together with the        stream comprising CO from step 4 into the oxygenate synthesis        reactor of step 2, and    -   6. reintroducing at least part of stream D into the syngas        reactor of step 1.

The term ‘target alcohols’, as used herewith and hereinafter, isunderstood to mean the alcohols produced (stream E) according to theprocess described by the present invention and preferably consist ofeither ethanol or propanol(s) or, more preferably, a mixture thereof.

The hydrocarbon feedstock used for syngas generation is preferably acarbonaceous material, for example biomass, plastic, naphtha, refinerybottoms, crude syngas (from underground coal gasification or biomassgasification), smelter off gas, municipal waste, coal, and/or naturalgas, with coal and natural gas being the preferred sources, and naturalgas being the most preferable source.

Natural gas commonly contains a range of hydrocarbons (e.g. C1-C3alkanes), in which methane predominates. In addition to this, naturalgas will usually contain nitrogen, carbon dioxide and sulphur compounds.Preferably the nitrogen content of the feedstock is less than 40 wt %,more preferably less than 10 wt % and most preferably less than 1 wt %.

Processes for producing mixtures of carbon oxide(s) and hydrogen(synthesis gas), in a syngas reactor, are well known. Each method hasits advantages and disadvantages, and the choice of using a particularreforming process is dictated by economic and available feed streamconsiderations, as well as obtaining the desired mole ratio of H2:CO inthe feedstock resulting from the reforming reaction. A discussion of theavailable synthesis gas production technologies is provided in both“Hydrocarbon Processing” V78, N. 4, 87-90, 92-93 (April 1999) and“Petrole et Techniques”, N. 415, 86-93 (July-August 1998), and arehereby incorporated by reference. It is also known that the synthesisgas may be obtained by catalytic partial oxidation of hydrocarbons in amicrostructured reactor as exemplified in “IMRET 3: Proceedings of theThird International Conference on Microreaction Technology”, Editor WEhrfeld, Springer Verlag, 1999, pages 187-196. Alternatively, thesynthesis gas may be obtained by short contact time catalytic partialoxidation of hydrocarbonaceous feedstocks as described in EP 0303438.The synthesis gas can also be obtained via a “Compact Reformer” processas described in “Hydrocarbon Engineering”, 2000, 5, (5), 67-69;“Hydrocarbon Processing”, 79/9, 34(September 2000); “Today's Refinery”,15/8, 9 (August 2000); WO 99/02254; and WO 200023689.

The syngas used in the present invention is preferably obtained via asteam reforming. Typically, for commercial syngas production thepressure at which the synthesis gas is produced ranges fromapproximately 1 to 100 bar, preferably 20 to 30 bar and the temperaturesat which the synthesis gas exits the reformer ranges from approximately700 DEG C. to 1000 DEG C. The high temperatures are necessary in orderto produce a favourable equilibrium for syngas production, and to avoidmetallurgy problems associated with carbon dusting. The synthesis gasused in the present invention preferably contains a molar ratio of(H2-CO2):(CO+CO2) ranging from 0.8 to 3.0, which is heavily dependent onthe hydrocarbon feedstock used. When natural gas is used as thehydrocarbon feedstock, the syngas obtained has a (H2-CO2):(CO+CO2)maximum ratio of 3.

The steam reforming reaction is a highly endothermic in nature. Thereaction is commonly catalysed within tubes of a reformer furnace. Wherenatural gas is the feedstock, the endothermic heat is usually suppliedexternally by firing additional amounts of natural gas. Simultaneous tothe steam reforming reaction, the water/gas shift reaction also takesplace. The presence of a catalyst in this reaction commonly requires ade-sulphurised feedstock, as sulphur compounds are known poisons for thetypical catalysts employed. The steam reformer requires a high steam tocarbon ratio to prevent carbon from being deposited on the catalyst andalso to ensure high conversion to carbon monoxide and the preferredmolar ratio of steam to carbon (i.e. the carbon that is present ashydrocarbons) is between 1 and 2.5, preferably between 1.2 and 2 andmost preferably between 1.4 and 1.8.

According to a preferred embodiment of the present invention, thehydrocarbon feedstock fed into the syngas reactor is preheated to atemperature comprised between 400 and 550 DEG C, and more preferably thepreheated temperature is such that it alleviates the formation of metaldusting (i.e. a temperature that is as close to 550 DEG C as possible).The use of a furnace(s) may be employed to generate the energy requiredto preheat the hydrocarbon feedstock prior to entering the syngasreactor. Alternatively, an interchanger may be employed in addition tothe furnace(s), whereby the heat generated from cooling the product fromthe syngas reactor (stream A), is then used to preheat the hydrocarbonfeedstock entering into the syngas reactor, thereby reducing the duty onthe furnace and increasing the overall heat efficiency of the process.Whilst use of the interchanger is the preferred method of operation, itshould be noted that stream A must be rapidly cooled (e.g. by preferablyusing a fluid) to prevent metal dusting; hence the maximum temperatureof the cold-side fluid (e.g. water) used to cool the exit stream isapproximately 500 DEG C. The preferred method of cooling stream A isagainst a boiling fluid, such as water.

According to the present invention, the exit stream obtained from thesyngas reactor (e.g. using a steam reformer), stream A, comprisesessentially a mixture of carbon oxide(s) and hydrogen. It can alsocomprise water, nitrogen and traces of unconverted hydrocarbon (e.g.C1-C3 alkanes). The stream A is then preferably cooled further to atemperature that is comprised between 5 and 60 DEG C, and morepreferably to a temperature that is comprised between 20 and 50 DEG C.Once this temperature has been achieved, then the majority of the wateris preferably removed from stream A and the overall water content of thetreated stream A, after water removal treatment, is less than 5% wt ofstream A, more preferably less than 1% wt of stream A and mostpreferably treated stream A contains less than 0.5% wt of water.

Treated stream A is then preferably pre-heated, by use of a furnace(s)and/or any other suitable method known to those skilled in the art, to atemperature that is comprised between the operating temperature of theoxygenate synthesis reactor and (or equal to) 30 DEG C less than theoperating temperature of the oxygenate synthesis reactor, morepreferably treated stream A is pre-heated to a temperature that is asclose to the operating temperature of the oxygenate synthesis reactor aspossible.

In one embodiment of this invention at least part, preferably all ofstream A comprising the desired synthesis gas molar ratio of (H2):(CO)is fed into the oxygenate synthesis reactor at a controlled rate and thereaction is carried out in a reaction zone under controlled conditionsof temperature and pressure and in the presence of a catalyst to convertthe feedstock into the target alcohols.

According to the present invention, the desired synthesis gas molarratio (defined as being H2/CO) of the total feed introduced into theoxygenate synthesis reactor of step 2, is preferably comprised between0.5 and 2.0, more preferably comprised between 0.5 and 1.5.

According to a preferred embodiment of the present invention, stream Ais passed through a H2/CO2 membrane prior to entering the oxygenatesynthesis reactor.

The H2/CO2 membranes that can be used according to the present inventionare preferably membranes based on a polymer packaged as a hollow fibre.A differential pressure is established across the said membrane. Allgases permeate from the high-pressure (feed) side of the membrane to thelow-pressure (permeate) side, and the difference in the permeation ratesof gases provides the separation. Molecules that permeate quickly, suchas H2, He, and H2S, can be separated from molecules that permeate moreslowly, such as CO, CH4 and N2. Such membrane technologies can be foundin ‘Purification and Recovery Options for Gasification’ D. J. Kubek, E.Polla, F. P. Wilcher, UOP, 1996, and are hereby incorporated byreference.

Optionally, after the gas is passed through the membrane some remixingof the permeate with the retained material may be employed in order toadjust the syngas ratio to achieve the optimum ratio required for theoxygenate synthesis reaction.

The oxygenate synthesis reaction (alcohol(s) synthesis), according tostep 2 of the present invention, is preferably performed by passing amixture of hydrogen and carbon monoxide (stream A) over a conversioncatalyst as a vapour phase reaction (e.g. using a fixed bed and/orfluidized bed reactor) or as a liquid phase reaction in an essentiallyinvolatile and inert solvent, such as a hydrocarbon (e.g. using a slurryreactor).

The said oxygenate synthesis reaction (the alcohol synthesis) may becarried out in a oxygenate synthesis reactor, under conditions asindicated in step 2. The term oxygenate synthesis reactor as used in thepresent invention pertains to any appropriate reactor, e.g. a tubularreactor using a fixed bed of the catalyst. The reactants may be fedupwards or downwards to the catalyst, or a combination of both, to afixed bed located in a tubular reactor. The reaction may be effected ina dynamic bed of the catalyst. In such a reaction, the bed of catalystis moving such as in the case of a fluid bed of the catalyst. Theoxygenate synthesis reactor may preferably be chosen amongst tubular,multitubular, slurry, moving bed, fluidised bed, radial bed, multibed orreactive distillation reactor. According to an embodiment of the presentinvention, a fixed bed reactor is used, preferably a radial bed(s) or amultitubular vapour phase reactor or a combination thereof is used. Mostpreferably the oxygenate synthesis reactor comprises a series ofadiabatic fixed bed reactors operated in either a longitudinal and/orradial flow mode.

According to a preferred embodiment of the present invention, thealcohol(s) produced in the oxygenate synthesis reactor (i.e. duringalcohol synthesis) are primarily methanol, ethanol, propanol(s)(n-propanol with low amounts of iso-propanol), and butanol(s) (n-butanoland iso-butanol); said methanol, ethanol, propanol(s) and butanol(s)preferably represent together at least 50% by carbon content of theproducts (where the products are defined as being all products excludingCO2 and CO) obtained from the oxygenate synthesis reactor (stream B),more preferably at least 75% by carbon content of the products obtainedand most preferably at least 80% by carbon content of the productsobtained.

According to another embodiment of the present invention esters andethers are also produced in the oxygenate synthesis reactor and togetherwith the alcohol(s) on a single pass, preferably represent at least 70%by carbon content of the products (where the products are defined asbeing all products excluding CO2 and CO) obtained from the oxygenatesynthesis reactor (stream B), more preferably at least 80% by carboncontent of the products obtained and most preferably at least 85% bycarbon content of the products obtained. Stream B also typicallycontains a level of nitrogen, which arises as an impurity from theaforementioned hydrocarbon feedstock(s), together with a level ofhydrocarbons (e.g. C1-C3 alkanes(s)) that arise from incompleteconversion in the reforming stage and as reaction by-products during theoxygenate synthesis reaction.

According to a preferred embodiment of the present invention thequantity of inert materials with respect to the oxygenate synthesisreaction (e.g. C1-C3 alkanes and nitrogen) present in stream B, duringnormal operation, is less than 30 mol % of stream B and preferably lessthan 20 mol % of stream B.

The C2 and C3 target alcohols comprise together, at least 25% by carboncontent of the products (where the products are defined as being allproducts excluding CO2 and CO), obtained from the oxygenate synthesisreactor (stream B), preferably at least 33% by carbon content of theproducts obtained and most preferably at least 50% by molar carboncontent of the products obtained.

In a preferred embodiment of the present invention, the conversion ofthe carbon oxide(s) per pass through the oxygenate synthesis reactor isset to operate between 5 and 70%, preferably between 10 and 50% and mostpreferably between 15 and 40%, as the applicants have found this to bethe most advantageous conversion rate in terms of sufficientproductivity of the target alcohol(s) per pass whilst maintainingreduced overall alkane production. Conversions per pass, higher thanthose stated above are covered by the present invention; however they donot represent preferred embodiments of the present invention since theylead to the undesirable formation of alkanes as part of the integratedprocess.

The temperature in the oxygenate synthesis reaction zone isapproximately between 150 and 400 DEG C, preferably between 250 and 350DEG C and most preferably between 280 and 320 DEG C.

The pressure employed in the oxygenate synthesis reaction zone may beselected from the approximate range of 20 to 200 bar, more preferably apressure is employed in the approximate range of 80 to 150 bar.Primarily, the hydrogen and carbon monoxide partial pressures present instream A should be sufficient to enable the production of the targetalcohols. For the purpose of this invention, the term GHSV is the gashourly space velocity which is the rate of gas flow over the catalyst.It is determined by dividing the volume of gas (at 25° C. and 1atmosphere) which passes over the catalyst in one hour by the volume ofthe catalyst.

The optimum gas hourly space velocity (GHSV) of the stream A (liters ofstream/hr/liter of catalyst) passing through the reaction zone can varysignificantly, depending upon a variety of factors such as, for example,reaction conditions, composition of the stream and age and type ofcatalyst being used. Preferably, the GHSV can be maintained at any ratein the range of from approximately 1 to 30,000 hr-1, more preferably theGHSV will be maintained at a rate of between approximately 500 hr-1 and20,000 hr-1, and most preferably the GHSV will be maintained at a rateof approximately between 1,000 hr-1 and 10,000 hr-1.

Whilst the aforementioned reaction conditions specified for theoxygenate synthesis reactor, form preferred embodiments for the presentinvention, reaction conditions outside of this stated range are notexcluded, and the effective reaction conditions may comprise any thatare sufficient to produce the aforementioned target alcohols. The exactreaction conditions will be governed by the best compromise betweenachieving high catalyst selectivity, activity, lifetime and ease ofoperability, whilst maintaining the intrinsic reactivity of the startingmaterials, the stability of the starting materials in question and thestability of the desired reaction product.

As previously indicated, the catalyst used in the oxygenate synthesisreactor is preferably a modified molybdenum sulphide based catalyst, ora modified methanol based catalyst and/or a precious metal basedcatalyst such as a rhodium catalyst, and/or a modified Fischer-Tropschcatalyst.

Molybdenum sulphide based catalysts are preferred; these can be modifiedby a promoter. Promoter(s) can be added as salts during the catalystpreparation; the preferred promoter(s) are potassium ions and arederived from a salt of potassium, such as potassium carbonate oracetate. The preferred loadings of potassium ions per molybdenum iscomprised between 0.7 and 1.5, most preferably between 1.0 and 1.4.

The preferred catalyst, according to the present invention, is amolybdenum sulphide based catalysts containing cobalt, the cobalt tomolybdenum molar ratio being preferably comprised between 0.5 and 3.0,more preferably between 0.5 and 1.0, most preferably between 0.5 to 0.9.

According to an embodiment of the present invention, stream B exitingthe oxygenate synthesis reactor is subsequently cooled and a separationinto a liquid portion and a gaseous portion is conducted. According to apreferred embodiment of the present invention the said separation isconducted using a knockout drum or a dephlegmator at a similar pressureto that used for the oxygenate synthesis reaction.

Subsequently, a C2 and C2+ alcohol(s) and water stream is recovered fromthe said separated liquid portion to form a stream E (e.g. byconventional distillation). Simultaneously, the said separated gaseousportion from stream B is preferably washed with alcohol, allowingrecovery of a CO2 rich stream D and the production of the gaseous partof stream C.

The efficiency of the said alcohol wash can be improved by pre-chillingthe alcohol. The said alcohol is preferably taken from the separatedliquid portion of stream B. The preferred alcohol used for performingthe wash is methanol, which can be obtained via the said conventionaldistillation of stream B.

The alcohol washing requires good gas/liquid contact. Common methodsused include vessel internals which increase internal surface area ofcontact between liquid and gas, such as packings, structured packings,baffles, sieve plates. Alternatively, said CO2 rich stream D may berecovered by any suitable method(s) known to those skilled in the art,for example, by reacting with amines; by performing a methanol wash(i.e. the RECTISOL process) and/or by using hot potassium carbonate(e.g. the BENFIELD process).

According to the present invention stream C comprises CO, C1-C3 alkanes,hydrogen and methanol. The said methanol comes from the separation ofthe liquid portion of stream B (post stream E recovery) and/or liquidmethanol recovered from the aforementioned CO2 washing.

Additionally, as a consequence of the aforementioned separation somemethanol may become entrained together with the CO2 to form a part ofstream D; this said methanol may then be recovered to subsequently forma part of stream C. The method used to recover the entrained methanolfrom stream D may be any one or more of the methods known to thoseskilled in the art (e.g. by using a H2O wash and/or by using molecularsieves and/or by using refrigeration techniques).

Thus, stream C consists of a gaseous part and a liquid part (understandard temperature and pressure, i.e. 0 C and 101,325 Pa). The liquidpart of stream C contains predominately methanol and may also containesters and/or ethers. The gaseous part of stream C predominatelycontains H2, CO, and alkanes (e.g. C1 to C3 alkanes); additionally itmay also contain N2.

According to the present invention, at least part of said stream C isreintroduced into the oxygenate synthesis reactor of step 2 preferablyby admixing at least part of stream C to treated stream A, prior toentering the oxygenate synthesis reactor.

According to a preferred embodiment of the present invention, after thesaid admixing of the recycle stream C and the treated stream A, at leastof part of the CO2 present is removed, by any suitable means or methodsknown to those skilled in the art; prior to the stream being introducedinto the oxygenate synthesis reactor of step 2. Alternatively at least apart of the said admixed stream may be introduced directly into theseparation stage defined by step 3, together with stream B.

The said recycle of stream C, results in an increased ester content inthe oxygenate synthesis reactor and the applicants have unexpectedlyfound that when a certain amount of esters are present in the oxygenatesynthesis reactor, there is an overall increase in the yield of thetargeted C2 and C2+ alcohol(s). Thus according to a preferred embodimentof the present invention, the preferred quantity of esters (as a molarratio of the total esters to methanol introduced into the oxygenatesynthesis reactor) introduced into the oxygenate synthesis reactor ofstep 2, is more than 0.1% but less than 10%, preferably more than 0.25%but less than 15% and most preferably more than 0.5% but less than 1%.

According to a further embodiment of the present invention, the saidquantity of esters that are present in the oxygenate synthesis reactor,may additionally comprise a separate independent feed of ester(s) (inaddition to those esters that are produced inside the oxygenatesynthesis reactor and form part of the liquid portion of the stream Crecycle) as part of the integrated process. Preferably the esters thatare introduced into the oxygenate synthesis reactor are those with 3 orless carbon atoms (i.e. 3 or less carbon atoms in either the alkylcomponent and/or 3 or less carbon atoms in the carboxylate component ofthe ester), most preferably the esters that are introduced into theoxygenate synthesis reactor are methyl acetate and/or ethyl acetate.

According to another embodiment of the present invention, the oxygenatesynthesis reactor advantageously contains a certain quantity ofmethanol. However, the preferred quantity of methanol present in theoxygenate synthesis reactor is preferably restricted, as it has beendiscovered that its presence leads to an increased production of methaneand hence, the beneficial effect of methanol addition on productivityreaches a plateau. Therefore, the applicants have found that thepreferred quantity of methanol (as a molar ratio of methanol to thetotal feed entering into the oxygenate synthesis reactor), entering intothe oxygenate synthesis reactor is more than 0.25% and less than 10%,preferably more than 0.5% and less than 5% and most preferably more than0.75% and less than 4%. The methanol may comprise a separate independentfeed of methanol, in addition to the said recycled methanol that forms apart of the liquid portion of stream C.

The applicants have unexpectedly found that by implementing thispreferred embodiment of separating and recycling the methanol into theoxygenate synthesis reactor as part of the integrated process of thepresent invention, it was possible to increase the amount of ethanol andpropanol(s) produced in the process. Thus, the present invention alsoprovides an improved process for the conversion of hydrocarbons toalcohol(s), in terms of efficiency and selectivity to the targetalcohol(s).

According to another embodiment of the present invention, at least partof the methanol that is present in stream C and/or stream E isrecovered, by any method or means known to those skilled in the art.

Depending on the feedstock and the selectivity for the conversion of thesyngas to alcohol(s), the applicants have discovered an additionalembodiment of the present invention, wherein it is advantageous to purgesome of steam C to prevent the build up of inert materials present inthe oxygenate synthesis reaction, e.g. methane, ethane and N2.

According to the present invention, a fraction of stream C, preferably afraction of the gaseous part of stream C, is treated and separated intoa stream comprising CO and a stream comprising H2 and inert componentscomprising alkanes and optionally nitrogen. The separated CO is thenrecycled to the oxygenate synthesis reactor of step 2 together with atleast part of the original stream C.

The part of the gaseous part of stream C which is directly recycled intothe oxygenate synthesis reactor of step 2 preferably represents from 95to 30% of the gaseous part of stream C, more preferably from 75 to 50%of the gaseous part of stream C.

The fraction of the gaseous part of stream C (step 4) which is treatedand separated preferably represents from 5 to 60% of the gaseous part ofstream C, more preferably from 25 to 40% of the gaseous part of streamC.

Preferably the separated hydrogen is recycled into the syngas reactor ofstep 1. Preferably the separated inert components (with respect to theoxygenate synthesis reaction, e.g. C1-C3 alkanes and optional nitrogen)are used as a fuel, more preferably the inert components are used as afuel for the furnace of the said syngas reactor.

The fraction of the gaseous part of stream C (step 4) which is treatedand separated may also still contain some methanol which is preferablyrecycled together with the separated CO into the oxygenate synthesisreactor of step 2.

As indicated above, there is a preferred total amount of methanol whichis recycled into the oxygenate synthesis reactor of step 2.Consequently, some of the methanol can also advantageously be separatedand exported for sale; it can also be used as a feed to the steamreformer of step 1 and/or used as a fuel.

The aforementioned separation of the fraction taken from stream C, intoa CO stream and a hydrogen stream and inert components, can be done byany appropriate methods known by those skilled in the art. The saidseparation can be done in one or several steps. For example, the COstream can be isolated from the combined H2 and inert components stream,said combined stream being either used as a fuel or then subjected to afurther separation stage in order to isolate the H2 from the inertcomponents which would then allow to use the H2 as a feedstock to theSMR. Alternatively, a preferred embodiment of the present invention isto proceed with the separation of the three streams in one step. Forexample, cryogenic separation can be advantageously used to recover C0and H2, from alkanes and nitrogen. Vacuum swing adsorption can also beused for this separation.

Alternatively, the applicants have unexpectedly found another embodimentin order to prevent the build up of inert materials inside the oxygenatesynthesis reactor. This embodiment consists of adding an independentwater feed to at least a fraction of stream C, preferably to at least afraction of the gaseous part of stream C, and subjecting the resultingmixture to a water gas-shift reaction step, in order to convert amajority of the CO present, into CO2 and H2. This then means that theseparation of CO2 and H2 from the inert components is economicallyadvantageous in terms of efficiency, by using a simple, yet effective,separation method known to those skilled in the art; for example, theCO2 can first be removed by an alcohol wash and the remaining part ofthe fraction of stream C can then undergo a membrane separation methodto isolate the H2. Alternatively, the original fraction of stream C isdirectly subjected to a membrane separation method which allows toseparate the CO2 and the H2 from the inert components.

Consequently, the recovered H2 and/or CO2 can advantageously be recycledback to the steam reformer of step 1.

Such appropriate membrane technologies can be found in ‘Purification andRecovery Options for Gasification’ D. J. Kubek, E. Polla, F. P. Wilcher,UOP, 1996, and are hereby incorporated by reference.

Another description of appropriate membrane separation technology isgiven by “Basic Principles of membrane technology by MarcelMulder—publisher Kluwer academic publishers 2000, London” ISBN0=7923-4248-8. Suitable membranes for hydrogen separation includeasymmetric or composite membranes with an elastomeric or glassypolymeric top layer. This top layer is typically ˜0.1 to a um inthickness. Suitable top layer membrane materials include elastomers suchas polydimethylsiloxane, and polymethylpentene, and glassy polymers suchas polyimides and polysulphone. Metal membranes such as palladium mayalso be employed and these are typically operated at elevatedtemperatures and as such maybe suitable for combined water gas shift andhydrogen recovery as a single unit operation. The driving force for theseparation is provided by a pressure drop across the membrane, hydrogenis recovered on the low pressure side and the CO2 and methane andnitrogen mostly retained on the high pressure side. Preferably themembrane material is a glassy polymer. Preferably the pressure dropacross the membrane is >5 barg and less than 100 Barg, the temperatureof operation is typically ambient to 80 C.

As indicated above, the water gas shift reaction is used to convertcarbon monoxide to carbon dioxide and hydrogen through a reaction withwater e.g.CO+H2O═CO2+H2

The reaction is exothermic, which means the equilibrium shifts to theright at lower temperatures conversely at higher temperatures theequilibrium shifts in favour of the reactants. Conventional water gasshift reactors use metallic catalysts in a heterogeneous gas phasereaction with CO and steam. Although the equilibrium favours formationof products at lower temperatures the reaction kinetics are faster atelevated temperatures. For this reason the catalytic water gas shiftreaction is initially carried out in a high temperature reactor at350-370 C and this is followed frequently by a lower temperature reactortypically 200-220 C to improve the degree of conversion (Kirk-Othmer1995, Ullman's 1989). The conversions of CO are typically 90% in thefirst reactor and a further 90% of the remaining CO is converted in thelow temperature reactor. Development of higher activity water gas shiftcatalysts will allow reduction in the reaction temperatures employed.Other non metallic catalysts such as oxides and mixed metal oxides suchas Cu/ZnO are known to catalyse this reaction. The degree of conversionof the CO can also be increased by adding more than the stoichiometricamount of water but this incurs an additional heat penalty. Methane andnitrogen are inert under typical water gas shift conditions. Then, atleast a fraction of stream C is fed to a water gas shift reactortogether with steam, preheated to the reaction temperature and contactedwith the catalyst, a second low temperature water gas shift reactor isoptionally employed on the cooled exit gas from this reactor.

Thus, according to another embodiment of the present invention, there isprovided a process for the conversion of a hydrocarbon feedstock intoalcohol(s), wherein the hydrocarbons are first converted into syngas,which is subsequently converted into alcohols, characterised by thefollowing consecutive steps:

-   -   1) converting a hydrocarbon feedstock, in a syngas reactor, into        a stream A, comprising essentially of a mixture of carbon        oxide(s) and hydrogen,    -   2) converting at least part of stream A, in the presence of a        catalyst in a oxygenate synthesis reactor under a temperature        comprised between 150 and 400° C. and a pressure of 20 to 200        bar, into an alcohols stream B, comprising essentially methanol,        ethanol, propanol(s), H2, C1-C3 alkanes, CO, CO2 and water,    -   3) separating stream B, into a stream C containing the CO, C1-C3        alkanes, H2 and methanol; a stream D containing the CO2; and        recovering a stream E containing the ethanol, propanol(s) and        water,    -   4) adding water to at least a fraction of stream C and        subjecting the resulting mixture to a water gas-shift reaction        step in order to convert a majority of the CO present into CO2        and H2,    -   5) separating the C1-C3 alkanes from the CO2 and H2 stream of        step 4,    -   6) recycling the H2 and CO2 stream from step 5 into the steam        reformer of step 1,    -   7) reintroducing at least part of stream C into the oxygenate        synthesis reactor of step 2, and    -   8) reintroducing at least part of stream D into the syngas        reactor of step 1.

As indicated above, the water gas-shift reaction step 4) is preferablyperformed on a fraction of the gaseous part of stream C only. The partof the gaseous part of stream C which is directly recycled into theoxygenate synthesis reactor of step 2 preferably represents from 95 to30%, more preferably from 83 to 50% of the gaseous part of stream C.

The fraction of the gaseous part of stream C (step 4) which is subjectedto the WGS treatment of step 4 preferably represents from 5 to 60% ofthe gaseous part of stream C, more preferably from 17 to 40% of thegaseous part of stream C.

According to the present invention, the said CO2 rich stream D producedin step 3, is preferably compressed and at least part of the stream isrecycled back to the syngas reactor of step 1, as a means of adjustingthe syngas ratio of stream A to the optimum ratio required for theoxygenate synthesis reaction. Therefore, the CO2 produced during theseparation of stream B (step 3) is not released to the atmosphere andmay be utilised in an environmentally efficient manner as well asimproving the overall economics of the system.

The applicants have unexpectedly found that an additional independentCO2 import may be required in order to provide the optimum syngas ratiofor the oxygenate synthesis reaction. The quantity of CO2 that needs tobe imported into stream D is between 0.02 and 1 TONNE(S) of CO2 perTONNE of C2 and C3 alcohol(s) produced, more preferably between 0.1 and0.5 TONNES of CO2 per TONNE of C2 and C3 alcohol(s) produced and is mostpreferably 0.38 TONNES of CO2 per TONNE of C2 and C3 alcohol(s)produced. In practice, the optimum quantity of CO2 imported will varydepending on the feedstock used for the syngas generation and for thesteam reforming furnace. For example, when hydrogen is used to fuel thefurnace(s), the overall CO2 emissions for the process will reach aminimum.

Indeed, importing CO2 quantities outside of the above stated ranges arealso included, however they do not form preferred embodiments of thepresent invention, since the applicants have found that when using acertain feedstock to fuel the furnace (e.g. hydrocarbons), introducinglevels of CO2 above those stated above into stream D can lead to theundesirable effect of increasing the overall dilute CO2 emissions forthe process.

The process according to the present invention has been found to behighly beneficial towards alcohol(s) selectivity, especially towardsethanol selectivity, whilst simultaneously significantly reducingoverall CO2 emissions and improving on the overall heat efficiencyassociated with conventional processes.

Beyond these advantages, the present process invention has also beenfound to encompass the following unexpected advantages, amongst others:

-   -   (i) less waste, and thus higher carbon efficiency.    -   (ii) reduced methane production.    -   (iii) improved economics, fewer separations, reduced storage        tanks.    -   (iv) no corrosion and metallurgy constraints due to the        potential hydrolysis of the esters during subsequent        purification and storage stages.

1. Process for the conversion of a hydrocarbon feedstock intoalcohol(s), wherein the hydrocarbons are first converted into syngas,which is subsequently converted into alcohols, comprising the followingconsecutive steps: 1) converting a hydrocarbon feedstock, in a syngasreactor, into a stream A, comprising essentially of a mixture of carbonoxide(s) and hydrogen, 2) converting at least part of stream A, in thepresence of a catalyst in a oxygenate synthesis reactor under atemperature comprised between 150 and 400° C. and a pressure of 20 to200 bar, into an alcohols stream B, comprising essentially methanol,ethanol, propanol(s), H2, C1-C3 alkanes, CO, CO2 and water, 3)separating stream B, into a stream C containing the CO, C1-C3 alkanes,H2 and methanol; a stream D containing the CO2; and recovering a streamE containing the ethanol, propanol(s) and water, 4) treating a fractionof stream C in order to separate said fraction into a stream comprisingCO, and a stream comprising H2 and the C1-C3 alkanes, 5) reintroducingat least part of stream C together with the stream comprising CO fromstep 4 into the oxygenate synthesis reactor of step 2, and 6)reintroducing at least part of stream D into the syngas reactor ofstep
 1. 2. Process for the conversion of a hydrocarbon feedstock intoalcohol(s), wherein the hydrocarbons are first converted into syngas,which is subsequently converted into alcohols, comprising the followingconsecutive steps: 1) converting a hydrocarbon feedstock, in a syngasreactor, into a stream A, Comprising essentially of a mixture of carbonoxide(s) and hydrogen, 2) converting at least part of stream A, in thepresence of a catalyst in a oxygenate synthesis reactor under atemperature comprised between 150 and 400° C. and a pressure of 20 to200 bar, into an alcohols stream B, comprising essentially methanol,ethanol, propanol(s), H2, C1-C3 alkanes, CO, CO2 and water, 3)separating stream B, into a stream C containing the CO, C1-C3 alkanes,H2 and methanol; a stream D containing the CO2; and recovering a streamE containing the ethanol, propanol(s) and water, 4) adding water to atleast a fraction of stream C and subjecting the resulting mixture to awater gas-shift reaction step in order to convert a majority of the COpresent into CO2 and H2, 5) separating the C1-C3 alkanes from the CO2and H2 stream of step 4, 6) recycling the H2 and CO2 stream from step 5into the syngas reactor of step 1, 7) reintroducing at least part ofstream C into the oxygenate synthesis reactor of step 2, and 8)reintroducing at least part of stream D into the syngas reactor ofstep
 1. 3. A process according to claim 1, wherein the syngas reactor ofstep 1 is a steam reformer and steam is fed into the said reactortogether with the hydrocarbon feedstock.
 4. A process according to claim1, wherein the synthesis gas molar ratio, defined as being H2/CO, of thetotal feed introduced into the oxygenate synthesis reactor of step 2, iscomprised between 0.5 and 2.0.
 5. A process according to claim 1,wherein the alcohol(s) produced in the oxygenate synthesis reactor ofstep 2, are primarily methanol, ethanol, propanol(s) (n-propanol withlow amounts of iso-propanol), and butanol(s) (n-butanol and iso-butanol)and represent together at least 50% by carbon content of the products,where the products are defined as being all products excluding CO2 andCO, obtained from the oxygenate synthesis reactor (stream B).
 6. Aprocess according to claim 1, wherein the conversion of the carbonoxide(s) per pass through the oxygenate synthesis reactor is between 5and 70%.
 7. A process according to claim 1, wherein recycle stream Ccomprises a liquid part containing methanol, esters and/or ethers, and agaseous part containing hydrogen, CO, nitrogen and C1 to C3 alkanes. 8.A process according to claim 7, wherein the quantity of esters,calculated as a molar ratio of the total esters to methanol introducedinto the oxygenate synthesis reactor, introduced into the oxygenatesynthesis reactor of step 2, are more than 0.1% but less than 10%.
 9. Aprocess according to claim 7, wherein the esters that are recycled intothe oxygenate synthesis reactor are those with 3 or less carbon atoms ineither the alkyl component and/or 3 or less carbon atoms in thecarboxylate component of the ester.
 10. A process according to claim 1wherein the separated hydrogen from step 4 is recycled back to syngasreactor of step 1 together with the CO2 recycle stream D.
 11. A processaccording to claim 1 wherein the separated inert components (C1-C3alkanes and nitrogen) of step 4 are used as a fuel.
 12. A processaccording to claim 1 wherein step 4 is performed on the gaseous part ofstream C.
 13. A process according to claim 2 wherein the syngas reactorof step 1 is a steam reformer and steam is fed into the said reactortogether with the hydrocarbon feedstock.
 14. A process according toclaim 1 wherein the synthesis gas molar ratio, defined as being H2/CO,of the total feed introduced into the oxygenate synthesis reactor ofstep 2 is comprised between 0.5 and 1.5.
 15. A process according toclaim 1 wherein the alcohol(s) produced in the oxygenate synthesisreactor of step 2 are primarily methanol, ethanol, propanol(s)(n-propanol with low amounts of iso-propanol), and butanol(s) (n-butanoland iso-butanol) and represent together at least 75% by carbon contentof the products where the products are defined as being all productsexcluding CO2 and CO obtained from the oxygenate synthesis reactor(stream B).
 16. A process according to claim 1 wherein the alcohol(s)produced in the oxygenate synthesis reactor of step 2 are primarilymethanol, ethanol, propanol(s) (n-propanol with small amounts ofiso-propanol) and butanol(s) (n-butanol and iso-butanol) and representtogether at least 80% by carbon content of the products, where theproducts are defined as being all products excluding CO2 and CO,obtained from the oxygenate synthesis reactor (stream B).
 17. A processaccording to claim 1 wherein the conversion of the carbon oxide(s) perpass through the oxygenate synthesis reactor is between 10 and 50%. 18.A process according to claim 1 wherein the conversion of the carbonoxide(s) per pass through the oxygenate synthesis reactor is between 15and 40%.
 19. A process according to claim 7, wherein the quantity ofesters, calculated as a molar ratio of the total esters to methanolintroduced into the oxygenate synthesis reactor, introduced into theoxygenate synthesis reactor of step 2, are more than 0.25% but less than15%.
 20. A process according to claim 7, wherein the quantity of esterscalculated as a molar ratio of the total esters to methanol introducedinto the oxygenate synthesis reactor, introduced into the oxygenatesynthesis reactor of step 2, are more than 0.5% but less than 1%.
 21. Aprocess according to claim 7, wherein the esters that are introducedinto the oxygenate synthesis reactor are methyl acetate and/or ethylacetate.
 22. A process according to claim 11, wherein the separatedinert components (C1-C3 alkanes and nitrogen) of step 4 are used as fuelfor the furnace used to preheat the hydrocarbon feedstock entering intothe syngas reactor.